Wheel construction has shown a very wide range of development since the earliest days of vehicle production. Beginning with wooden spokes based on carriage wheels and then on to spokes made of metal, for decades vehicle wheels had been produced from stamped steel. This type of wheel proved both reliable and cost-effective.
However, as both wheel appearance and overall vehicle weight reduction became more important in vehicle design, the ubiquitous stamped steel wheel has generally been replaced by wheels cast from a material such as aluminum, at least in the passenger vehicle sector. Cast aluminum wheels can be formed into many designs and generally provide reduced weight while providing structural integrity.
For all of their benefits, cast aluminum wheels do present challenges to both manufacturers and designers. This is because cast aluminum wheels are required to balance strength, stiffness and part mass. On the one hand, wheel forging can improve the material properties (strength) and reduce mass. However, wheel stiffness may be sacrificed in the process. Wheel geometry can be used to improve these properties but casting and subsequent machining of the wheel limit the usefulness of geometry. For example, it is difficult to make hollow wheel spokes or to create functional shapes that provide aerodynamic benefits.
The design and production of aluminum wheels are not the only challenges faced by wheel designers and manufacturers. Customer satisfaction with regard to today's cast aluminum wheel is generally high but dissatisfaction has been expressed over such wheels having poor scratch resistance. This is particularly frustrating given the considerable expense faced by the consumer in the initial purchase of the cast aluminum wheel. Over time cast aluminum wheels show damage from contact with curbs, road debris and gravel roads. In response, some wheel manufacturers as well as after-market auto parts suppliers offered a spray-on clear coat to resist such damage. However, such clear coat arrangements for wheels have proven to only resist minimal damage before scratching.
In view of the state of the art, it may be advantageous to provide a wheel having both reduced weight and increased scratch resistance without compromising aesthetic qualities. As in so many areas of automobile manufacturing technology, there is always room for improvement in both the design and production of vehicle wheels.